Bug 693372

Summary:	[RHEL6.0] "virsh attach-device" doesn't attach a device with a specified name.
Product:	Red Hat Enterprise Linux 6	Reporter:	asilva <asilva>
Component:	libvirt	Assignee:	Libvirt Maintainers <libvirt-maint>
Status:	CLOSED NOTABUG	QA Contact:	Virtualization Bugs <virt-bugs>
Severity:	medium	Docs Contact:
Priority:	medium
Version:	6.0	CC:	ajia, dallan, dyuan, eblake, jmunilla, skito, weizhan
Target Milestone:	rc
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2011-06-02 21:12:22 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	658636

Description asilva 2011-04-04 13:20:48 UTC

> Description of Problem:

"virsh attach-disk" doesn't attach a disk with a specified name. The name of the virtual device attached by the command run according to "Step to Reproduce" is an unexpected one. We believe that this unexpected behavior is due to a bug of the said command. Could you please fix it so that a device name can be specified as expected?

Architecture: x86_64
Kernel Version: kernel-2.6.32-71.el6.x86_64
Related Package Version: libvirt-client-0.8.1-27.el6.x86_64

> How reproducible:
Always

> Step to Reproduce:

1) Start a guest OS.

# virsh start <domain-id>

2) Confirm that there is neither "vdb" nor "vdd" on the guest domain.

$ ls /dev/vd*
/dev/vda
/dev/vda1
/dev/vda2
/dev/vda3

3) Run "virsh attach-disk" with the above xml file.

# virsh attach-disk <domain-id> /dev/sdb2 vdd
Disk attached successfully

4) Confirm what name the virtual device on the guest domain is.

guest$ ls /dev/vd*
/dev/vda
/dev/vda1
/dev/vda2
/dev/vda3
/dev/vdb
~~~~~~~~~
<The virtual device's name is not the specified "vdd" but "vdb".>


> Actual Results:

"virsh attach-disk" doesn't attach a disk with a specified name.

> Expected Results:

"virsh attach-disk" attaches a disk with a specified name.

> Hardware configuration:
Model: Fujitsu PRIMEQUEST 1800
CPU Info: Intel(R) Xeon(R) CPU E7540 2.00GHz
Memory Info: 16GB

Comment 1 asilva 2011-04-04 13:30:32 UTC

Step1:
host# virsh attach-disk rhel6-x86-64 /dev/sdb1 vdd
Disk attached successfully

Step2:
> additional information

guest# ls /dev/vd*
/dev/vda

Log:
10:21:00.139: debug : qemuDomainPCIAddressSetNextAddr:2278 : PCI addr 0:0:0 already in use
10:21:00.139: debug : qemuDomainPCIAddressSetNextAddr:2278 : PCI addr 0:0:1 already in use
10:21:00.139: debug : qemuDomainPCIAddressSetNextAddr:2278 : PCI addr 0:0:2 already in use
10:21:00.139: debug : qemuDomainPCIAddressSetNextAddr:2278 : PCI addr 0:0:3 already in use
10:21:00.139: debug : qemuDomainPCIAddressSetNextAddr:2278 : PCI addr 0:0:4 already in use
10:21:00.139: debug : qemuDomainPCIAddressSetNextAddr:2278 : PCI addr 0:0:5 already in use
10:21:00.139: debug : qemuDomainPCIAddressSetNextAddr:2283 : Allocating PCI addr 0:0:6
10:21:00.139: debug : qemuMonitorAddDrive:1897 : mon=0x7ff5ec0015f0 drive=file=/dev/sdb1,if=none,id=drive-virtio-disk3,format=raw
...
10:21:00.147: debug : virJSONValueToString:1059 : result={"execute":"device_add","arguments":{"driver":"virtio-blk-pci","bus":"pci.0","addr":"0x6","drive":"drive-virtio-disk3","id":"virtio-disk3"}}

Comment 2 Shinji Kito 2011-04-05 02:06:23 UTC

Additional Note:
1. When a device is detached, index of vd* is not decremented.
   This causes vd* keeps incremented when you attach a device.
   BZ: https://bugzilla.redhat.com/show_bug.cgi?id=692767

   I already verified the fix with an attached patch.

2. When <target> is specified in virsh, for example, 
   virsh attach-disk <domain> <source> <target>, 
   simply gets omitted.

   We see the same result with "attach-device".

   http://libvirt.org/formatdomain.html#elementsDisks
   
   [target]
    The target element controls the bus / device under which the disk is 
    exposed to the guest OS. The dev attribute indicates the "logical" 
    device name. The actual device name specified is not guaranteed to map 
    to the device name in the guest OS. Treat it as a device ordering hint. 
    The optional bus attribute specifies the type of disk device to emulate; 
    possible values are driver specific, with typical values being "ide", 
    "scsi", "virtio", "xen" or "usb". If omitted, the bus type is inferred 
    from the style of the device name. eg, a device named 'sda' will typically 
    be exported using a SCSI bus. Since 0.0.3; bus attribute since 0.4.3; 
    "usb" attribute value since after 0.4.4

   As you can see from the above link, "target" is used just as a hint,
   assigning specific device names in kernel layer is not a common approach,
   and it would be better to assign names via userland such as udev.


Engineering, please let us know how you are going to fix this issue.
   Updating man page, and/or, disabling target option, or something else?

Comment 3 Dave Allan 2011-04-05 03:25:22 UTC

Per the documentation you quoted, this functionality is working as designed:

"The actual device name specified is not guaranteed to map to the device name in the guest OS."

Given that we've already documented that it's not guaranteed to be honored, there's nothing more we can do here.  Device naming in the guest is dependent on the guest OS.